Jitter is a deviation or displacement of pulses in a high-frequency digital or analog signal. As the name suggests, jitter can be thought of as shaky pulses. Jitter is the variation of an event from its ideal position in time. Among the causes of jitter are electromagnetic interference and crosstalk with other signals. Jitter can cause a display monitor to flicker, affect the ability of the processor in a personal computer to perform as intended, introduce clicks or other undesired effects to audio signals, and cause the loss of data transmitted between network devices.
Measuring transmitter jitter of high speed input/outputs (I/Os) is one of the most complicated production tests. The complexity is due to the ambiguous ways to measure the jitter, the high frequency of the transmitted signal and the external dedicated instrument that gets the signal, post processes it, and provides an output as its' jitter. Yet, the importance of this parameter is critical, since according to the jitter value, the robustness of the transmitted signal is tested, and one concludes the chip's performance on real (customer) systems according to the jitter value. In one way to measure the jitter of a signal, one samples it in high frequencies, and via post processing, estimates a difference between the actual transitions and the theoretical transitions. The higher the signal's frequency is—the test becomes more important and difficult to implement, and the instrument that measures the jitter becomes more complex and expensive. Traditionally, signal frequencies rise over time, therefore the challenge is growing.
In conservative ways, transmit jitter is measured by a unique ad hoc external instrument attached to a tester.
There is a need for improved circuits and methods for testing integrated circuits for jitter.